I don't get why you say it is a pure PvP ability. Granted it is extremely usefull for PvP, but that doesn't make it PvP exclusive. Just taking Kara as an example.
Attumen, you can stay at over 20 yards in the first half of this fight, but the second half it's completely useless since you have to stand right on his butt to avoid the charge.
Moroes, distance doesn't matter, so staying at over 20 yards should be easy.
Maiden, I don't think the bottom stair is 20 yards away, so I will count this fight as the ability being useless.
All the opera events, there is no reason you can't be at over 20 yards away.
Curator, if you have enough DPS you can send your pet on curator and easily stay 20 yards away while you take out the orbs. If not at the very least you will have the extra DPS for when he innervates.
Ilhoof, again no reason you can't be at over 20 yards
Shade, the room is big enough to where if Aran is in the exact center, you have 22.5 yards to the wall(45 yard diameter according to wowhead), so staying at over 20 yards shouldn't be much of an issue, of course you will be sucked in and running out and moving from the blizzards, but overall more usefull than not.
Netherspite is questionable. More often than not I was put into a blue beam rotation with another hunter, so we were somewhere within the 5-10 yard range, so I will count this fight as a no for the ability.
Nightbane you should be at max range to avoid the fear and that is more than 20 yards, so this ability is extremely usefull for this fight.
Prince, again you want to be at max range to avoid the shadow nova.
So in Kara alone that is 8.5 out of 10 fights where this ability is more usefull than not for such a big increase in DPS. To go a little farther, both the High King and Gruul can be fought at max range, so there is another raid that it is usefull in.
Granted we don't know what the raid fights are going to be like at 80, but as examples of raids we have now, this is an extremely usefull talent for both PvP and PvE. But if this talent is more usefull or less usefull than the talents you will be scrificing to get this one is another matter entirely.